The worldwide interoperability for microwave access (WiMAX) is a wireless metropolitan area network (MAN) technology based on the IEEE802.16 standard. The WiMAX network wireless side is a wireless MAN access technology based on the IEEE802.16d/e standard and adopts the orthogonal frequency division multiplexing (OFDM) and OFDM access (OFDMA) physical layer technology, which can effectively resist multipath fading. At the optimal channel fading condition, the transmission speed may approach 75 Mbps.
The entire WiMAX network mainly includes three parts, namely, a user terminal, an access service network (ASN), and a connectivity service network (CSN).
(1) The user terminal is a subscriber station (SS) or a mobile station (MS), which is provided for a user to access the WiMAX network.
(2) The ASN is defined as a network function collection for providing wireless access services for the WiMAX user terminal. The ASN includes a base station (BS) network element and an ASN gateway (ASN-GW) network element. The main functions of the BS network element include providing a Layer 2 (L2) connection between a BS and a user terminal, a radio resource management, and so on. The main functions of the ASN-GW network element include providing a client function for the user terminal authentication, authorization, and accounting functions, and providing a relay function (for example, IP address allocation), or intra-ASN handover of Layer 3 (L3) information for the user terminal.
(3) The CSN is defined to provide an IP connection service for the WiMAX user terminal. The CSN mainly includes logical entities such as a pre-paid server and an authentication, authorization and accounting (AAA) server. The main functions provided by the CSN include IP address allocation for the user terminal, Internet access, AAA proxy or AAA server, a user terminal-based authorization control, and so on.
In order to realize the mobility restriction of the user terminal, a mobility access classifier is added to the subscription relation of the user and includes fixed, nomadic, and mobile services. The mobile service means that when the user terminal moves within the coverage of the network side at a certain speed, the user terminal can use the data service of the network continuously, and the network side supports the handover of the user terminal and ensures the session continuity during the handover. The nomadic service means that the user terminal can access the network at different geographic locations. During the data service session, the user terminal is usually attached to a certain access network fixedly, and when the user terminal moves to a new location, it is required to access the network once again, so as to realize a new data service session. Therefore, the user terminal of the nomadic service is enabled to initiate the re-attachment of the device, but does not necessarily ensure the session continuity. The fixed service means that the user terminal can merely access the network in a fixed area for realizing the data service, and when the user terminal leaves the fixed area, the user terminal cannot access the network.
As for certain operators in some countries, due to the license restrictions, the operators can merely operate fixed or nomadic network services. Therefore, the mobility of the user terminals for the fixed and nomadic users is required to be restricted.
The inventor(s) of the present invention found that, in the prior art, after a mobile user terminal roams to a visited network with mobility restriction, or roams to a network without mobility restriction from a network with mobility restriction, for example, after the mobile user terminal roams to a network merely supporting fixed or nomadic users, or after a nomadic network user terminal roams to a network without mobility restriction, the mobility type of the roaming user terminal cannot be determined, so that the roaming user terminal cannot access a network with mobility restriction, or the user terminal of the network with mobility restriction cannot access a network without mobility restriction.